The present invention relates generally to semiconductor devices, and more particularly to semiconductor devices formed having dual gate dielectric thicknesses and utilizing high-k gate dielectric materials such as metal oxides.
In integrated circuit manufacturing, there is often a need to form transistors with different gate dielectric thicknesses on the same semiconductor substrate or wafer. For example, transistors for input/output (I/O) devices may require thicker gate dielectrics than, e.g., transistors used for the core logic. A conventional process for forming differing thickness is called a DGO process, which stands for Dual Gate Oxide. In a conventional DGO process, a xe2x80x9cthickxe2x80x9d silicon dioxide layer (e.g. for the I/O devices) is formed and a resist mask is used to mask the thick silicon dioxide layer in the I/O regions. The thick silicon dioxide layer is then etched away or otherwise removed from the unmasked region, where the core logic devices are to be formed. The mask is removed and a thin silicon dioxide layer is then grown over the core logic device region. The gate electrode material, typically polysilicon, is then deposited over the substrate, which at this point includes gate dielectrics of two different thicknesses. The gate electrode material and gate dielectrics are then patterned and etched to form the gate electrode and oxide stack of each transistor.
The DGO process described above has found acceptance in the industry as a manufacturable and cost effective way of producing transistors having two different gate dielectric thicknesses. However, as transistor sizes shrink there is a move in the semiconductor industry to replace traditional silicon dioxide gate dielectrics with higher-k dielectric materials (i.e. dielectrics having higher dielectric constants), such as metal oxides. But because metal oxides cannot be thermally grown on a silicon substrate as silicon dioxide can, there are problems associated with multiple metal oxide depositions to form differing oxide thicknesses and with etching of the metal oxide if one were to attempt to merely substitute a metal oxide for silicon dioxide in a conventional DGO process. Accordingly, there is a need for a semiconductor manufacturing process in which dual gate dielectric thicknesses can be achieved with metal oxides or other high-k dielectric materials.